The present invention relates generally to the field of disc drive storage devices, and more particularly, but not by way of limitation, to supplying power from a spindle motor in a disc drive system.
Modern hard disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a high speed. Information is read from and written to each disc in a plurality of concentric tracks by a transducer assembly mounted on an actuator arm. The outside circumference of each disc is referred to as the xe2x80x9couter diameterxe2x80x9d (OD), and the center of each disc is referred to as the xe2x80x9cinner diameterxe2x80x9d (ID). A transducer assembly is said to xe2x80x9cflyxe2x80x9d over the disc surface as the disc rotates. When disc rotation velocity decreases, the layer of air supporting the transducer assembly above the disc surface diminishes and the assembly descends toward the disc surface. However, contact between the transducer assembly and the disc surface can damage the magnetizable medium and the transducer assembly. Furthermore, through a phenomenon called xe2x80x9cstiction,xe2x80x9d a transducer assembly can become temporarily xe2x80x9cstuckxe2x80x9d to the disc surface after contact with the disc surface. Stiction can damage the magnetizable medium, the transducer assembly, and/or the actuator arm when the disc drive system initiates disc rotation in an attempt to move the transducer assembly from the disc surface.
One approach to addressing this problem is to land the transducer assembly in a textured landing zone, preferably near the ID of the disc. Typically, data is not recorded in the landing zone, and the texturing of the landing zone surface minimizes stiction. The actuator arm is moved to an ID landing zone from the disc when the rotational velocity of the disc is decreased, thereby avoiding contact with the data area of the disc. The transducer assembly is moved back to the disc when the rotational velocity increases to allow it to fly above the disc surface.
An alternative approach for loading/unloading a transducer assembly is to move the actuator arm onto a ramp, preferably positioned outside the OD of the disc. The ramp supports the transducer assembly outside the diameter of the disc and prevents contact between the transducer assembly and the disc surface. An actuator arm typically sweeps a 25xc2x0 arc from ID to OD to access tracks on a disc; however, the ramp feature can increase the total sweep (i.e., stroke) required of the actuator arm and a voice coil motor (VCM) to approximately 50xc2x0. Furthermore, the ramp presents additional resistance to the movement of the actuator arm, because the arm must ascend the sloped surface of the ramp, which also introduces an additional friction component.
A rotary VCM actuator, shown generally at 100 in FIG. 1, commonly provides the motive force to move the actuator arm 102, and therefore the transducer assembly 104, across the disc from ID to OD. The actuator arm 102 is cantilevered outward over the disc surface 106 from a common pivot structure 108, while the coil 110 of the VCM 100 extends horizontally outward from the other side of the pivot structure. A permanent magnet and pole piece structure 112 is fixedly mounted to the housing 114 of the disc drive in such an arrangement that the coil 110 is movably supported in the middle of the magnetic field formed by the stationary magnet of the structure 112.
Sophisticated control logic uses a servo algorithm to apply carefully calculated amounts and polarities of DC (direct current) power to the ends of the coil 110 for controllably moving the coil 110 within the magnetic field, thereby moving the actuator arm 102 across the disc surface 106. As the coil 110 moves between the horizontal extremes of the stationary magnet in structure 112, the actuator arm 102 moves across the disc surface 106 approximately between the ID and the OD. As such, the length of the stationary magnet structure 112 corresponds proportionally to the arcuate sweep of the actuator arm 102.
In disc drive designs employing storage of the transducer assembly 104 outside of the OD, the length of the stationary magnet structure 112 is commonly increased to accommodate the increased sweep of the actuator arm. At the horizontal extremes of the stationary magnet structure 112, the torque generated by the VCM is weaker than toward the horizontal interior of the VCM because the flux density is diminished. Applied torque is proportional to both flux density and current in the coil 110. Accordingly, the torque applied to the actuator arm 102 by a particular DC current (i.e., as controlled by a particular servo algorithm) is diminished near the extremes of the actuator arm""s sweep. In disc drive designs employing ramped storage of the actuator arm 102 outside of the OD, the diminished torque presents a difficulty moving the actuator arm 102 onto a ramp 116. Even in the circumstance of a control power-down operation, the diminished torque outside the OD impacts the unloading of the transducer assembly to a ramp by requiring additional current from the power supply and/or changes in the servo algorithm.
The diminished torque may be addressed by increasing the length of the stationary magnets in structure 112 to extend the magnetic field at the outer extreme of the sweep. However, merely increasing the length of the magnets increases the cost and size of the components. Increasing the magnet length also decreases the flux density distributed between the poles. Therefore, to apply the same torque to the actuator arm 102 during normal operation, additional current must be supplied to the actuator coil 110, unnecessarily increasing the normal power consumption of the disc drive system. The problem is how to provide adequate torque to the actuator arm 102 when it is needed to ascend the ramp 116 outside the OD of a disc surface 106 during a retract operation without unnecessarily increasing the cost, size, and, the overall power consumption of the disc drive system during normal operation.
Embodiments of the present invention provide a method and system for unloading a transducer assembly to a ramp positioned outside an outer diameter of a disc in a disc drive system using supplementary power from back EMF generated by a spindle motor rotating from a velocity that exceeds the normal operating velocity.
In accordance with the preferred embodiment, a method for unloading a transducer assembly to a ramp positioned outside an outer diameter of a disc in a disc drive system including a spindle motor for rotating the disc and a positioning coil coupled to a power supply for moving the transducer assembly relative to the disc is provided. The disc is rotated at a first rotational velocity equaling a normal operational rotational velocity of the disc drive system. A retract signal is received. The rotation of the disc is accelerated to a second rotational velocity that exceeds the normal operational rotational velocity of the disc drive system, responsive to the retract signal. Power is decoupled from to the spindle motor. The positioning coil is energized with output from the power supply to retract the transducer assembly to the ramp, responsive to the retract signal. The positioning coil is also energized with back voltage generated from the spindle motor to retract the transducer assembly to the ramp.
In accordance with the present invention, a disc drive system for unloading a transducer assembly from a disc is provided. A spindle motor rotates the disc at a first rotational velocity being a normal operational velocity of the disc drive system. A spindle motor control module removes power provided to the spindle motor. A positioning coil coupled to a power supply moves the transducer assembly relative to the disc. A back voltage switching module diverts back voltage generated from the spindle motor to supplement the power provided to the positioning coil by the power supply, responsive to a retract signal. A ramp is positioned outside the outer diameter of the disc to which the positioning coil unloads the transducer assembly when powered by the power supply and the back voltage.